In the bustling city of Zhengzhou, an innovative construction technique is being employed to ensure the safe and efficient passage of a metro line through challenging geological conditions. The artificial ground freezing (AGF) method is being utilized to stabilize a calcareous cemented stratum, and a recent study published in *Chengshi guidao jiaotong yanjiu* (Urban Rail Transit Research) sheds light on the temperature field variations and ground deformation laws observed during this process. Led by YE Qing of China Railway 11th Bureau Group Co., Ltd., the research offers valuable insights that could significantly impact future construction projects in similar strata.
The study focuses on the behavior of the temperature field and ground deformation during the freezing construction of a metro link passage. “When the AGF method is applied in different water-rich strata, the freezing characteristics of the frozen soil vary significantly,” explains YE Qing. “It is therefore necessary to study the variation of the temperature field and ground deformation law during the freezing construction process in a typical calcareous cemented stratum.”
The research involved a detailed arrangement of umbrella-shaped freezing holes and temperature measurement holes. Field measurements were conducted for brine temperature, measuring point temperature, and vertical displacement at ground monitoring points directly above and adjacent to the link passage during freezing excavation and thawing periods. The data collected revealed a consistent temperature drop trend across all measurement holes, which could be divided into four distinct stages: rapid cooling, phase transition, secondary cooling, and stable freezing.
One of the key findings was the difference in cooling rates between shallow and deep measuring points. “In the rapid cooling stage, shallowly embedded measuring points will cool faster than deeper ones, whereas the opposite is observed during the secondary cooling stage,” notes YE Qing. This understanding is crucial for optimizing the freezing process and ensuring the stability of the construction site.
The study also highlighted the differences in temperature variations between calcareous cemented strata and silty clay strata. While the temperature difference between different depth measurement points in calcareous cemented strata was relatively small, it was significantly larger in silty clay strata. This information is vital for engineers and construction professionals working in similar geological conditions.
During the excavation phase, the vertical displacement at monitoring points above and adjacent to the link passage varied considerably. The research emphasized the need for reinforcement grouting in the soil near the link passage central axis and its overlying region to control thaw-induced settlement. This finding has significant commercial implications for the energy sector, as it can help prevent costly delays and ensure the safety of construction projects in water-rich strata.
The insights gained from this research are expected to shape future developments in the field of artificial ground freezing. By understanding the temperature field variations and ground deformation laws, engineers can optimize the freezing process, improve construction efficiency, and minimize risks. This, in turn, can lead to more sustainable and cost-effective construction practices, benefiting the energy sector and other industries that rely on stable geological conditions.
As the demand for urban infrastructure continues to grow, the need for innovative construction techniques like AGF will only increase. The research conducted by YE Qing and his team at China Railway 11th Bureau Group Co., Ltd. provides a valuable contribution to the field, offering practical insights that can be applied to future projects. With the publication of this study in *Chengshi guidao jiaotong yanjiu*, the urban rail transit research community now has a deeper understanding of the temperature field variations and ground deformation laws during freezing construction in calcareous cemented strata, paving the way for more efficient and safe construction practices.